The measure on the June 8 ballot would put all candidates for statewide, congressional and legislative offices on the same primary ballot. Passage could potentially weaken party power.

Reporting from Sacramento — — Two days after he was finally sworn in as California's lieutenant governor after a grueling partisan battle, Republican Abel Maldonado appeared on national TV with political comedian Stephen Colbert to discuss his signature issue, a primary election designed to reduce the influence of party hardliners in the Legislature.

"Why on Earth would you want to destroy the two-party system?" demanded Colbert, who parodies a right-wing cable news host.

Leaders from both major parties in California, who vehemently oppose the open-primary measure, are asking essentially the same question, only they don't see it as a laughing matter.

Proposition 14, which appears on the June 8 ballot, would put all candidates for statewide, congressional and legislative offices on the same primary ballot and allow voters to choose from the full list. The top two vote-getters for each office — regardless of party — would face each other in a runoff.

A poll released Wednesday by the nonpartisan Public Policy Institute of California showed 60% of respondents in favor of the measure, 27% opposed and 13% undecided.

Backers, including Gov. Arnold Schwarzenegger, say the system would free candidates from the need to court the radical wings of their parties to win nomination to the November ballot. That, in turn, would lead to the election of more moderate lawmakers and more cooperation on tough issues like fixing California's $19.1-billion budget deficit.

Under the current system, Republicans vote on one ballot in a primary election and Democrats on another. Independents, who now represent a record 20% of the California electorate, are allowed to choose either ballot. But few do, so their influence in a primary is minimal, and candidates for November are generally chosen by hard-core party loyalists.

About a third of California congressional and legislative districts are dominated by a single party, according to a recent report by the nonpartisan Center for Governmental Studies in Los Angeles. Almost all are Democratic strongholds. In some, Democrats have such an advantage that the two top primary vote-getters might both be Democrats.

In those cases, Proposition 14 supporters said, they hope the more moderate candidate could win by appealing to Republicans and independents.

As of Friday, Schwarzenegger and the California Chamber of Commerce had helped raise more than $4.7 million for a Yes on 14 campaign, which has started airing a radio ad that claims the measure would reduce "the influence of the major parties which are now under the control of the special interests."

In a display of harmony that would seem unthinkable on other issues, leading state Democrats and Republicans announced a joint campaign to defeat the measure. They had raised $200,000 as of Friday.

"Both political parties in California hate this measure," said Tony Quinn, co-editor of the nonpartisan California Target Book, which tracks state political races. "They like having these little private clubs. But the voters don't."

Party leaders say passage of Proposition 14 would invite a slew of unintended consequences, including highercampaign costs and political skullduggery.

"It allows for mischief where Democrats could go and choose the Republican nominee," said John Burton, chairman of the state Democratic Party.

He said there are Democrats in safe districts who might try to help their party by casting their primary votes for hard-line Republicans who are "so far out" that they could not win a general election.

Under the current system, primary campaigns are less expensive than general elections because candidates have to woo only voters registered in their own party. With an open system, candidates would need to appeal to all voters, sending out a lot more mail and potentially buying expensive air time on radio and TV. The increased costs could drive them deeper into the arms of well-heeled special interests, party leaders say.

Those leaders also take issue with the underlying notion that they are a source of unhealthy division.

"Broad-based political parties are an essential part of our democracy," said California Republican Party Chairman Ron Nehring. "The alternative is to have voters divided by … region, or ethnicity or religion."

Burton, whose Democrats control both chambers of the Legislature, scoffed at the notion that he can call the shots for lawmakers.

"If I had power, this wouldn't even be on the ballot, because I urged the [Senate president] pro tem and the Assembly speaker not to do it," he said.

In fact, it was the Legislature that put the measure on the ballot after one lone moderate broke last year's budget stalemate. Maldonado, then a state senator, agreed to vote for tax increases after legislative leaders agreed to put the open-primary measure before voters.